Various types of electrocautery devices are used for ablating tissue. Typically, such devices include a conductive tip or blade which serves as one electrode in an electrical circuit which is completed via a grounding electrode coupled to the patient. With sufficiently high levels of electrical energy between the two electrodes, heat is generated which is sufficient to denature proteins within the tissue and cause cell death.
By controlling the energy level, the amount of heat generated and the degree of tissue damage can also be controlled. High levels of voltage can actually cut and remove tissue (i.e., electrosurgery), while lower levels will simply create sufficient heat to cause cell damage, but leave the structure intact (i.e., catheter ablation) and block electrical pathways within the tissue. Irrigation of the electrode(s) with saline or other conductive fluid can decrease the interface impedance, cool the tissue and allow for a greater lesion depth.
The treatment of chronic atrial fibrillation (AF) requires the creation of numerous linear lesions that extend completely through the thickness of the tissue. Some electrophysiologists have created these lesions using a tip electrode of standard ablation catheters. These catheters were designed to create spot lesions, typically for ablation of specific structures or focal abnormalities. In order to make the linear lesions required to replicate the MAZE procedure, an electrophysiologist makes a series of focal lesions, and “connects the dots.”
Manufacturers have therefore developed catheters that have a linear array of electrodes along a long axis (i.e., the Amazr, MECCA, and Revelation catheters). The catheter and electrodes can be positioned in contact with the tissue and either individually or sequentially apply energy to each electrode. Additionally, catheters which incorporate an electrode which is energized and moves along the length have been proposed.
Surgeons have also been able to create linear lesions on the heart using applications of the same techniques. For example, Kottkamp et al. in an article entitled “Intraoperative Radiofrequency Ablation of Chronic Atrial Fibrillation: A Left Atrial Curative Approach by Elimination of Anatomic ‘Anchor’ Reentrant Circuits,” Journal of Cardiovascular Electrophysiology, 1999; §10:772-780 disclosed using a hand-held device that creates as series of spot or short (<1 cm) linear lesions. Other investigators have used long, linear unipolar probes to create somewhat longer lesions, such as described by Shirmoikd E. et al. in an article entitled “In Vivo and In Vitro Study of Radio-Frequency Application with a New Long Linear Probe: Implication for the MAZE Procedure,” Journal of Thoracic and Cardiovascular Surgery, 2000; §120:164-72. Still others have used multi-electrode linear catheters, similar to those described above to create a series of ablations that net a linear lesion, as described by Melo J. et al. in an article entitled “Endocardial and Epicardial Radiofrequency Ablation in the Treatment of Atrial Fibrillation with a New Intra-Operative Device,” European Journal of Cardio-Thoracic Surgery, 2000; §18:182-186.
U.S. patent application Ser. No. 10/015,690, in the names of Francisichelli et al. describes a bipolar ablation device that integrates an electrode into jaws of a hemostat-like or forceps-like device, known as the Cardioblate-BP. This results in a tool that can clamp and ablate the tissue in between the jaws. In conjunction with a transmurality algorithm, this configuration is amenable to creating transmural lesions. However, the Cardioblate-BP was designed to access the heart via a mid-line sternotomy. In order for the therapy to be considered as stand-alone, access must be made less invasively. Simply placing the Cardioblate-BP jaw onto an endoscopic handle has certain advantages, but there are significant limitations when trying to manipulate both jaws simultaneously through separate tissue spaces.
A microwave device that can loop around the posterior of the heart to encircle the pulmonary veins has been developed. A right thorocotomy is created at about the fourth intercostal space, and the pericardium is freed behind the superior vena cava and the inferior vena cava. A moveable antenna slides within an integral sheath and discrete sections are ablated in series is described by Saltman, “AE in a Completely Endoscopic Approach to Microwave Ablation for Atrial Fibrillation,” Heart Surgery Forum, 2003, 6(3):E38-E41.
Today, the MAZE procedure is performed with traditional cut and sew techniques. The market is demanding quicker, safer and less invasive approaches. Many companies are developing ablation techniques that heat (or cool) and thermally destroy the underlying tissue. Methods of chemical ablation have also been proposed.